Application of inverse fluidization in wastewater treatment: From laboratory to full‐scale bioreactors

Abstract

The inverse fluidization is a new multiphase gas-liquid or gas-liquid-solid system. The first studies of two phase (liquid-solid) inverse fluidization were originally published independently by Shimodaira et al. [6], Nikolov et al. [5] and Fan et al. [2]. The main difference between the classic and inverse fluidization is that the solid particle density in the inverse fluidized bed is less than the density of the continuous fluid and therefore the bed is fluidized by a downflow of the fluid. Schematic illustration of both classic and inverse fluidized beds is shown in Figure 1. One of the most important recent applications of fluidized beds is in the field of bioreactor engineering. It is well known that almost all types of microorganisms spontaneously attach themselves to any inert solid surface in contact with the liquid growth media. The microorganisms use exopolysaccharide {open_quotes}bridges{close_quotes} to attach themselves to the solid support and to each other. This structure of microorganisms and exopolysaccharides is known as biofilm. The fluidized bed bioreactors are used primarily for processes in which the fluidized particles are used as an inert solid support. There is a problem when the biofilm microorganisms multiply and the biofilm thickness increase. This limits diffusion ofmore » oxygen and/or the organic substrate to the deeper layers of the biofilm. Starvation of the microorganisms at the base of the biofilm causes pieces of the biofilm to detach (Figure 2) and leads to ineffective bioreactor operation. The maximal biofilm thickness at which no diffusional limitation is observed (phase 3 in Figure 2), is usually around 100 {mu}m. Therefore, to operate the bioreactor efficiently, the biofilm thickness should be approximately 100 {mu}m. The use of inverse fluidization can solve this problem. 6 refs., 10 figs.« less